The present invention relates to a cylindrical roller bearing incorporated in a general machine such as a middle-size electric motor, a large-size electric motor, or the like, and particularly to a cylindrical roller bearing in need of low vibration and low noise.
As a vibration/noise reducing technique for a cylindrical roller bearing, for example, as shown in Japanese Utility Model Unexamined Publication No. Hei. 3-67718, there is known a technique in which a roller guide system is used as a system for guiding a cage so that the weight of the cage is loaded on rollers which are existed within unloading-zone (hereinafter refering unloading-zone rollers). The load of the weight of the cage is set against centrifugal force acting on rolling rollers so that the pressure of contact of rollers with an outer race is reduced. As a result, the motion of the unloading-zone rollers is restricted so that reduction of vibration/noise of the bearing is attained.
In a pressed cage for low vibration and low noise, generally, a roller guide surface d of a cage a is formed so as to be opposite to a crowning portion e of a roller rolling surface as shown in FIG. 7.
In the bearing vibration/noise reducing technique disclosed in Japanese Utility Model Unexamined Publication No. Hei. 3-67718, however, as shown in FIG. 8, the pitch circle diameter of pocket holes b of a cage a was set to be smaller than the pitch circle diameter of rollers c. Accordingly, if the bearing was produced with an improper difference between the pitch circle diameters, the restriction in the unloading zone by the cage a became intense. As a result, the rollers c interfered with the cage a superfluously. There was a disadvantage that impact noise (cage noise) was produced due to collision of the rollers c with the cage a.
Further, when the restriction by the cage a was intense, the bearing was apt to be affected by error in production of individual cages. Accordingly, vibration and noise levels of the bearing often scattered. Furthermore, since the guide system was limited to a roller guide system, the specification of the bearing was limited necessarily.
Further, since the roller guide surfaces d of the cage a were formed in portions, respectively, opposite to the crowning portions e on the roller rolling surface as shown in FIG. 7, rollers in the unloading zone in which the roller motion was limited by being guided by the cage a were made unstable by the crowning portions so that skew, or the like, occurred easily. As a result, there was a disadvantage that vibration/noise was produced in the bearing inclusive of the cage.
Note that an occurrence of this disadvantage is not limited by a type of guiding system of cage. This disadvantage is generated in a bearing having a cage of a race guiding system, as well.
The present invention is designed to solve the aforementioned disadvantages and an object of the present invention is to provide a cylindrical roller bearing in which not only squeaking noise caused by rubbing of rollers against inner and outer race surfaces in the unloading zone, cage noise caused by collision of rollers with the cage and vibration/noise of the bearing, inclusive of the cage, caused by occurrence of skew, or the like, can be prevented well but also variations in vibration and noise levels of individual bearings can be suppressed.